time_conversion.h

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#pragma once
 
#include <cstdint>
 
namespace esphome {
 
template<typename ReturnT = uint32_t>
__attribute__((always_inline)) inline constexpr ReturnT micros_to_millis(uint64_t us) {
  constexpr uint32_t d = 125U;
  constexpr uint32_t q = static_cast<uint32_t>((1ULL << 32) / d);  // 34359738
  constexpr uint32_t r = static_cast<uint32_t>((1ULL << 32) % d);  // 46
  // 1000 = 8 * 125; divide-by-8 is a free shift
  uint64_t x = us >> 3;
  uint32_t lo = static_cast<uint32_t>(x);
  uint32_t hi = static_cast<uint32_t>(x >> 32);
  // Combine remainder term: hi * (2^32 % 125) + lo
  uint32_t adj = hi * r + lo;
  // If adj overflowed, the true value is 2^32 + adj; apply the identity again
  // static_cast<ReturnT>(hi) widens to 64-bit when ReturnT=uint64_t, preserving upper bits of hi*q
  return static_cast<ReturnT>(hi) * q + (adj < lo ? (adj + r) / d + q : adj / d);
}
 
}  // namespace esphome